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issue 0152 RESOLVED: byte-promote sub-byte (Atomic(bool)) atomic load/store

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LLVM rejects a sub-byte atomic memory access (must be byte-sized), so
Atomic(bool) — bool lowers to i1 — failed verification on load/store. The
atomic emitters in src/backend/llvm/ops.zig now perform a sub-byte access in
its byte storage type (i8) and trunc/zext the value at the boundary (new
atomicByteType helper: i8 for .bool, null otherwise). rmw/cmpxchg are left
as-is on purpose — a bool rmw/CAS is rejected at the sx level (integer-only),
so a sub-byte element never reaches those emitters.

Regression test examples/1705-atomics-bool-byte-promoted.sx. Suite green 729/0.
Unblocks Future.canceled: Atomic(bool) in the B1.2 async layer.
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agra
2026-06-21 05:42:48 +03:00
parent ea1faf7b69
commit e5586f61b8
6 changed files with 86 additions and 4 deletions
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issues/0152-atomic-bool-sub-byte-atomic-llvm-reject.md
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# 0152 — `Atomic(bool)` emits a sub-byte (i1) atomic load/store that LLVM rejects
## ✅ RESOLVED (2026-06-21)
**Root cause** — the atomic load/store emitters in `src/backend/llvm/ops.zig`
used `toLLVMType(ty)` directly as the atomic access type. For a `bool`
element that is `i1`, which LLVM rejects for atomics (size must be a byte
multiple).
**Fix** — `emitAtomicLoad`/`emitAtomicStore` now promote a sub-byte element
to its byte storage type (`i8`) for the atomic access, and `trunc`/`zext`
the value at the boundary (a new `atomicByteType` helper returns `i8` for
`.bool`, null otherwise). rmw/cmpxchg were left unchanged on purpose: a
`bool` rmw/CAS is rejected at the sx level (`atomic.sx` — "requires an
integer type"), so a sub-byte element can never reach those emitters (a
comment records this). `bool` is the only sub-byte scalar in sx.
**Verified** — the repro prints `yes`; regression test
`examples/1705-atomics-bool-byte-promoted.sx` (init / store / reset round-
trip on `Atomic(bool)`). Full suite green (729/0).
**Downstream (NOT this bug):** with `Atomic(bool)` fixed, the B1.2 async
examples surfaced ANOTHER, separate bug — a generic value-failable
`($R, !E)` fn reached through a re-export alias loses its `!` error channel
at the call site (typed as a plain tuple), so `await(...) or { … }` builds a
malformed PHI. `io.sx`'s `await`/`IoErr` are re-exported via `std.sx`, so the
async surface is now blocked on THAT (filed as a new issue), not on 0152.
---
## Symptom
`Atomic(bool)` lowers `bool` to LLVM `i1` and emits the atomic load/store